1. Field of the Invention
This invention relates to a radiation image read-out apparatus for use in a radiation image recording and reproducing system. This invention particularly relates to a radiation image read-out apparatus which is made small by simplification of the mechanism in the apparatus.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318 and 4,387,428 and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use a stimulable phosphor in a radiation image recording and reproducing system. Specifically, a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet) is first exposed to a radiation passing through an object such as the human body to have a radiation image of the object stored thereon, and is then scanned with stimulating rays such as a laser beam which cause it to emit light in proportion to the stored radiation energy. The light emitted by the stimulable phosphor sheet upon stimulation thereof is photoelectrically detected and converted to electric image signals, and the radiation image of the object is reproduced as a visible image by use of the image signals on a recording material such as a photographic film, a display device such as a cathode ray tube (CRT), or the like.
In the aforesaid radiation image recording and reproducing system, the stimulable phosphor sheet is used to temporarily store a radiation image until the sheet is scanned with stimulating rays to read out the radiation image. Therefore, after the radiation image is read out from the stimulable phosphor sheet, radiation energy remaining thereon should be erased to reuse the sheet.
For satisfying this requirement, it has been proposed to provide a radiation image read-out apparatus with a read-out section for reading out an image stored on a stimulable phosphor sheet, and an erasing section for erasing radiation energy remaining on the sheet.
As such read-out apparatuses, there has been proposed an apparatus provided with the read-out section, the erasing section, and a cassette holding section for releasably holding a cassette which houses therein a single stimulable phosphor sheet carrying a radiation image stored thereon in the form housed in the cassette by use of an external image recording apparatus. In the proposed apparatus, the stimulable phosphor sheet is taken out of the cassette, sent to the read-out section and the erasing section for carrying out image read-out and erasing on the stimulable phosphor sheet, and then conveyed into the empty cassette at the cassette holding section. In the case where the stimulable phosphor sheet on which the image read-out and erasing have been finished is returned in this manner into the cassette in the read-out apparatus, a loader or the like for loading the cassette with the stimulable phosphor sheet outside of the read-out apparatus prior to the next image recording step becomes unnecessary. However, in this case, since the read-out apparatus is exclusively occupied by a single stimulable phosphor sheet until the sheet is housed in the cassette after image read-out and erasing are conducted on the sheet, processing of the next stimulable phosphor sheet cannot be started as long as processing of the preceding stimulable phosphor sheet is being carried out. Thus an unnecessarily long time is taken, and the processing capacity of the apparatus decreases markedly. Accordingly, in the radiation image read-out apparatus provided with the erasing section and constituted for loading the stimulable phosphor sheet into the cassette inside of the apparatus, it would be very advantageous if a stacker for temporarily housing the stimulable phosphor sheets therein and feeding out the housed sheets one by one could be provided in the sheet conveyance means present on the downstream side of the erasing section. In this case, exactly after the stimulable phosphor sheet has been taken out of the cassette, one of the erased reusable stimulable phosphor sheets can be fed out of the stacker and loaded into the cassette.
On the other hand, a stacker of the type as mentioned above should preferably be provided also between the cassette holding section and the read-out section. Specifically, a comparatively long time is taken for carrying out image read-out at the read-out section. Therefore, in the case where the stacker is provided on the upstream side of the read-out section, a plurality of image-recorded stimulable phosphor sheets can be accommodated in the stacker while the image read-out is being carried out for a single stimulable phosphor sheet at the read-out section, and it is possible to eliminate the problem that the image-recorded sheet is made to wait for a long time in the form housed in the cassette at the cassette holding section. Also, in the case where the stacker is provided, even though the read-out section becomes defective and inoperable, image recording in an external image recording apparatus need not be stopped immediately, but instead the image recording apparatus can be operated continuously for some period.
However, the aforesaid stacker for accommodating a plurality of the stimulable phosphor sheets is comparatively large. Therefore, in the case where two such stackers are provided in the apparatus, the apparatus becomes large.